basic linux firewall

iptables -F
iptables –P INPUT DROP
iptables –A INPUT –I lo –j ACCEPT
iptables –A INPUT –m state –state ESTABLISHED,RELATED –j ACCEPT
iptables –A INPUT –m state –state NEW –p tcp –dport 22 –j ACCEPT
iptables –A INPUT –m state –state NEW –p udp –dport 53 –j ACCEPT
iptables –A INPUT –m state –state NEW –j DROP